Issue: The MQAttach Application Pool is not of the correct .NET Version
Solution:
Step 1:
Start -> Control Panel -> Administrative Tools -> Internet Information Services Manager -> Expand your server -> Application Pools - MQAttach Pool
Right Click -> Basic Settings
Change the NET CLR Version to v2.0.0.x as shown below
Step 2
Start -> Control Panel -> Administrative Tools -> Internet Information Services Manager -> Expand your server -> Application Pools - MQAttach Pool
Right Click -> Advanced Settings
Change Enable 32-Bit Applications to True
Step 3
Restart IIS or the MQAttachPool